A Look at IPv6

With IPv6, IP addresses go from 32-bit to 128-bit. Here's why the change is being made.

Vinton Cerf and Bob Kahn came up with the
original version of TCP (Transmission Control Protocol, RFC 675;
December 1974) and Jon Postel with that of IP (Internet Protocol,
RFC 760; January 1980) 20 years ago and more. These increased the
network “address space” to 32 bits, but the structure of the
ARPANET was “classless”, that is, the hierarchical distributed
database we are familiar with came about only with Dave Mills'
conceptualization of the Domain Name System (DNS; RFC 799;
September 1981) and its implementation by Paul Mockapetris (RFCs
882 and 883; November 1983). Mockapetris' implementation was called
Jeeves. BIND (Berkeley Internet Name Daemon; written by Kevin
Dunlap, maintained by Paul Vixie) is currently the most-used.

Thus we achieved 32-bit addressing and a hierarchical array
of classes of networks: A, B, C, D and E. There are 128 Class A
addresses, each of which can have 16,777,216 unique host
identifiers. There are 16,384 Class B addresses with 65,536 unique
identifiers, 2,097,192 Class C addresses and over 268 million Class
D groups. Class E addresses have never been available for general
use.

Using this scheme, DNS allowed for about four billion hosts
on 16.7 million networks. This seemed like a very large number of
addresses. But the expansion of Internet use over the past decade
has been explosive.

In August 1990, during the Vancouver Internet Engineering
Task Force (IETF) meeting, Frank Solensky, Phill Gross and Sue
Hares projected the current rate of assignment would exhaust the
Class B space by March of 1994.

Classless Inter-Domain Routing (CIDR, RFCs 1518 and 1519;
September 1993) was introduced to improve both routing scalability
and address-space utilization in the Internet. By eliminating the
notion of “network classes”, CIDR allows for a better match
between address requirements and address allocation. CIDR has
enabled the Internet to function while growth continues.

Even with CIDR, it was revealed at the July 1994 Toronto
meeting of the IETF that the Internet would exhaust the IPv4
address space between 2005 and 2011. With several more years of
experience, we can push these dates out a bit, but exhaustion will
come.

The Internet has grown with the number of intranets (what we
used to think of as “internal corporate networks”) and the number
of different uses to which they are put (Internet radio, telephone,
mobile computing, etc.).

The Toronto IETF meeting set up an “IPng” (Internet
Protocol Next Generation) or “IPv6” task force, cochaired by
Scott Bradner and Allison Mankin. Recommendations from that task
force were released in October 1994 for discussion at the December
1994 IETF meeting. The basic goal was to have something in place
before 2000, so that the time limit would not be pushed.
Unfortunately, as Bradner and Mankin put it in their
recommendation:

Some people pointed out that this type of
projection makes an assumption of no paradigm shifts in IP usage.
If someone were to develop a new “killer application” (for
example cable TV set-top boxes), the resultant rise in the demand
for IP addresses could make this an overestimate of the time
available.

IPv6 provides for 128-bit addressing. This is a gigantic
number, larger than the estimated total number of molecules in the
moon. Just how this will work is still unclear; as I write this,
the new protocol has yet to be widely deployed. Among other things,
going from 32 to 128 bits will entail renumbering a large number of
addresses already in use.

However, it is absurd to state that address space depletion
is the only driving force behind IPv6. While the address space now
provided for is enormous, it's not everything. A number of other
abilities “have been developed in direct response to current
business requirements for more scalable network architectures,
mandatory security and data integrity, an additional field for
quality-of-service (QoS), autoconfiguration and more efficient
network route aggregation at the global backbone level.”--IETF
draft; no longer on-line.

A business or private user might well say “So what?” to
this, thinking that IPv6 support for a large variety of network
devices just isn't an end-user or business concern.

Over the next few years, conventional computers on the
Internet will be joined by a variety of new devices, including
palmtop personal data assistants (PDA), hybrid mobile-phone
technology with data processing capabilities, smart set-top boxes
with integrated web browsers, and embedded network components in
equipment ranging from office copy machines to kitchen appliances.
Many devices requiring IP addresses and connectivity will be
consumer-oriented, such as your coffee machine, dishwasher,
etc.

IPv6's 128-bit address space will allow businesses to deploy
a huge array of new desktop, mobile and embedded network devices in
a cost-effective, manageable manner. Furthermore, IPv6's
autoconfiguration features will make it feasible for large numbers
of devices to attach dynamically to the network, without incurring
unsupportable administration costs for an ever-increasing number of
adds, moves and changes. The business requirement for IPv6 will be
driven by end-user applications.

Peter H. Salus, the author
of A Quarter Century of UNIX and Casting the Net, is Editorial Director of Linux Journal.